Build A Frequency Counter With ICM7216

The lCM7216 has been designed for use in a wide range of Universal and Frequency counters. In many cases, prescalers will be required to reduce the input frequencies to under 10MHz. Because INPUT A and INPUT B are digital inputs, additional circuitry is often required for input buffering, amplification, hysteresis, and level shifting to obtain a good digital signal.

Build A Frequency Counter With ICM7216

The lCM7216B can be used as a minimum component complete Universal Counter as shown in Figure 1. This circuit can use input frequencies up to 10MHz at INPUT A and 2MHz at INPUT B. If the signal at INPUT A has a very low duty cycle it may be necessary to use a 74LS121 monostable multivibrator or similar circuit to stretch the input pulse width to be able to guarantee that it is at least 50ns in duration.

To measure frequencies up to 40MHz the circuit of Figure 2 can be used. To obtain the correct measured value, it is necessary to divide the oscillator frequency by four as well as the input frequency. In doing this the time between measurements is also lengthened to 800ms and the display multiplex rate is decreased to 125Hz.

If the input frequency is prescaled by ten, then the oscillator can remain at 10MHz or 1MHz, but the decimal point must be moved one digit to the right. Figure 3 shows a frequency counter with a ÷10 prescaler and an lCM7216A. Since there is no external decimal point control with the lCM7216B, the decimal point may be controlled externally with additional drivers as shown in Figure 3. Alternatively, if separate anodes are available for the decimal points, they can be wired up to the adjacent digit anodes. Note that there can be one zero to the left of the decimal point since the internal leading zero blanking cannot be changed. In Figure 4 additional logic has been added to count the input directly in period mode for maximum accuracy. In Figures 3 and 4, INPUT A comes from QC of the prescaler rather than QD to obtain an input duty cycle of 40%.